It is known to provide WDM optical communications networks in the form of rings or interconnected rings. Typically these are bidirectional rings using two or four fibers. Various automatic protection switching schemes are known. For example, in a BLSR protection scheme, in the event of a fault, wavelengths travelling in one direction around the ring are switched to another fiber to enable them to reverse direction around the ring to reach their destination node.
It is known to use WDM optical networks for use in mobile backhaul networks. Current solutions for mobile backhaul networks may use L2/L3 switching with OEO (Optical-Electrical-Optical) conversion or microwave radio connections. The introduction of differentiated broadband services requiring low latency, the increase of the traffic load, the convergence of the mobile and fixed infrastructures, the need for sites consolidation and energy saving are all motivating the introduction of optical solutions in radio access and backhaul networks. This means packet processing is moved to the access and metro edge of the network and intermediate channel add-drop and ring interconnection is performed at the physical layer in the optical domain. Optical connections can help in saving energy, e.g. replacing switches for ring interconnection with ROADM based nodes or avoiding bridge sites. This is particularly so where protection is provided, in H-RAN parts for example. This implies equipment duplication.